1. Field of the Invention
The present invention generally relates to a method and apparatus for nano imprint lithography, and more particularly to a pneumatic method and apparatus for nano imprint lithography.
2. Description of the Related Art
The process of imprint lithography involves pressing a template (or mold or mask) against a polymer or photoresist-coated workpiece, curing the polymer and removing the template from the workpiece leaving behind an impression of the template in the cured polymer coating. The deformation of the template and/or workpiece under applied mechanical pressure is a problem when the features of the template are of very small (e.g., nanometer) dimensions and for which it is desirable to maintain long range dimensional tolerances on this scale.
Additionally, imperfections with respect to flatness (e.g., uniform thickness) of either the template or workpiece impose further constraints to printing nanometer-scale features.
The conventional methods and apparatus have used a rigid, thick glass or quartz template rigidly clamped (or glued rigidly) to a frame.
Finally, it is desirable to use a template that is a fraction of the dimension of the workpiece or substrate in order to meet alignment and template fabrication needs relating to nano scale lithography. Thus, the template is applied sequentially or stepped across the substrate to fill the substrate with patterns.
Thus, imprint lithography typically transfers a pattern from a thick block of quartz to a generally thinner workpiece, like a silicon wafer. However, as alluded to above, when performing imprint lithography, one attempts (ideally) to squeeze a liquid photoresist to an infinitely thin layer except for the feature(s) etched in the mask. Silicon wafers with “real world” chips (particularly after they have been processed) have some topography (e.g., hills and valleys on a long scale), and the chips may be slightly warped, etc. Thus, the silicon wafers typically are not perfectly flat. This is problematic.
Prior to the present invention, there has been no attempt to solve such a problem by using a transparent quartz template pressed in place against a workpiece using pneumatic pressure.
More specifically, there has been no apparatus or method in which pneumatic pressure is uniformly applied against either (or both) the quartz template and the workpiece to achieve uniform compression of the photoresist.
Hence, such methods have not been able to retain the essential transparent properties of the quartz template while applying uniform pressure to a conformal membrane, thereby allowing the compensation for planarity defects in both template and workpiece.
Other conventional methods have used a template made out of a flexible polymer material for the purpose of providing mechanical conformity between template and workpiece. Still other conventional methods have used a rigid quartz template, covered with a layer of soft polymer material. These methods have several major drawbacks, including that dimensional integrity in the plane of the template is not sufficiently preserved. Additionally, the motion of the polymer material due to non-uniform pressure or due to small temperature gradients generate distortions to the printed patterns that prohibit their use in microelectronic lithography.
While thermal curing is an option, there has been no conventional method which has adequately addressed the case (and the attendant problems) where the polymer is cured by exposure to ultraviolet light (UV). Additionally, ultraviolet (UV) transparency is severely degraded by the polymer material. Further, exposure to UV radiation degrades the polymer material over time.